My U.S. Pat. Nos. 4,711,659, 4,804,403, and 4,969,947 taught the concept of reacting layers of resins with central granules of water soluble plant foods to provide an attrition resistant controlled release plant food. Also disclosed were the uses of finely divided fillers between the layers of resin, and fillers dispersed in the resin forming monomers. The fillers taught were diluents applied in a variety of ways, usually as dry powders, and never by in-situ coreaction of water-soluble plant nutrients.
U.S. Pat. Nos. 4,369,055 and 4,881,963, Fujita et al, disclose methods of producing slow releasing coated fertilizers using resin coatings containing finely divided fillers, such as talc. No teachings were provided on in-situ reaction of water soluble plant nutrients to form slow releasing plant nutrients to aid the resin coating in resisting attrition of the coated granules.
Commercial delivery, handling, storage, and application of coated plant food granules require conveying, dumping, dropping, rolling, and blending. All of these operations subject the products to substantial attrition. Low integrity coatings, such as sulfur, catastrophically fail under severe handling conditions. Even with very good resin coated granules, as in the foregoing U.S. Patents, vigorous commercial handling reduces the integrity of the coatings. To preserve the desired release rate after attrition, a thicker coating might be used, but this increases costs and introduces wide variations in the actual release rates, depending upon the severity of handling and storage. In commercial practice wide variations in release rates are experienced, even with good resin coatings, particularly thin coatings, because of attrition variations caused by differences in handling and storage operations.
It is an object of this invention to provide a controlled release granular plant food composition which provides for improved attrition resistance by use of reinforced resin coatings on central particles of water soluble plant nutrients.
It is a further object of the invention to provide improved reinforcement of resin coatings by use of very finely divided water insoluble particles of plant nutrients formed in-situ by coreaction of water soluble plant nutrients in layers of water insoluble resin covering central particles of water soluble plant nutrients.
It is a further object of the invention to provide a method for preparing the improved reinforced resin coated attrition resistant controlled release granular plant food.